General combination locks for luggage cases have combination-changeability. However, in the prior art, the combination of the lock is changed by means of a pushing rod arranged beneath the base of the lock in such a way that sleeves on the shaft can be pushed and disengaged from combination dials by the pushing rod so that the combination dials can rotate freely and thus provide combination-changeability. The locks which are operated in this way are not widely used due to the complexity of the constituent parts, the high cost of manufacture, the disturbance of the combination caused by the contents of the case, and the trouble encountered during the combination changing operation. At present, the generally used locks are primarily characterized in that the pushing seat outside the combination lock can be used for combination changing purpose as long as it is pushed to a position in the same direction beyond the position for opening the lock. By this type of construction, it is more convenient than ever to accomplish the combination changing operation. However, it still has the drawback of combination disturbance caused by inadvertently pushing the seat forward.